PEROL LAKE, Peru, June 17 (Reuters) - Thousands of opponents of a $5 billion gold project of Newmont Mining circled a lake high in the Andes on Monday, vowing to stop the company from eventually draining it to make way for Peru's most expensive mine.

Lake Perol is one of several lakes that would eventually be displaced to mine ore from the Conga project. Water from the lakes would be transferred to four reservoirs that the U.S. company and its Peruvian partner, Buenaventura, are building or planning to build.

The companies say the reservoirs would end seasonal shortages and guarantee year-round water supplies to towns and farmers in the area, but many residents fear they would lose control of the water or that the mine would cause pollution.

"Hopefully, the company and the government will see the crowd here today and stop the project," said Cesar Correa, 28, of the town of Huangashanga in the northern region of Cajamarca.

He was one of many protesters who arrived at Lake Perol on foot or on horseback, some wearing ponchos, as well as traditional broad-brimmed straw hats or baseball caps.

Others carried blankets and bags of potatoes and rice - planning to camp out at the site for weeks to halt the project.

The company said about 1,000 protesters were present, though protesters said their flock swelled to 5,000 or 6,000. A Reuters witness estimated 4,000 people at the protest.

"Why would we want a reservoir controlled by the company when we already have lakes that naturally provide us water?" asked Angel Mendoza, a member of a peasant patrol group from the town of Pampa Verde.

The controversy over Conga - which many in the business sector see as essential for the country's bustling economy - has posed a major challenge to President Ollanta Humala during his nearly two years in office.

He has twice shuffled his cabinet in the face of violent protests against the project.

The protest on Monday was largely peaceful and there were no clashes with police, though a handful of protesters threw rocks and set fire to a wall near one reservoir.

Newmont and Buenaventura said in a statement: "As stated previously, we will only build the proposed Perol reservoir if we are able to secure all the necessary permits and complete an intensive public involvement process with neighboring communities."

"We respect everyone's right to safely and responsibly express their opinion, whether they oppose mining or support economic development," the statement said.

In May, a minor clash between protesters and police marked an ended nine months of relative calm when Humala's government said it would stop trying to overcome local opposition to the mine.

The new round of protests came after a top official for the Conga project, Chief Executive Roque Benavides of Buenaventura, told Reuters water from Perol would be transferred to a new reservoir later this year.

He later said the project might be in jeopardy if water from the lakes could not be transferred.